Cabriolet Roof Clean: Audi A4

This Audi A4 cabriolet came in for a hood clean and two-year nano protection coat -- and arrived with a bonus layer of cat hair. The owner's cat had been sleeping on the roof, which at least confirmed it was soft enough to nap on. Underneath the cat hair: the usual ground-in dirt, moss around the back window, and grime along the side rails.

The moss and green growth that builds up on a neglected convertible roof is not just a cosmetic problem. Dust and grit accumulate in the fabric fibres underneath, causing wear every time the hood moves. What looks like a surface cleaning job is also about preserving the roof itself -- a replacement hood is expensive, and most of the time one that has been properly maintained does not need replacing at all. On this car, once it was cleaned and dried, the roof looked good enough that it should see out the rest of the car's life.

Convertibles also have drainage channels built into the roof mechanism that most owners do not know exist. If they block, water backs up and finds its way into the car. We offer a drain flush as part of our roof cleaning service, along with rubber seal conditioning -- the seals dry out and shrink over time, and keeping them treated is one of the simplest ways to prevent leaks. On this car the owner had already been looking after the rubbers herself and chose to skip that part, which is exactly the right attitude.

We have cleaned hundreds of convertible roofs over the years and built up a set of techniques along the way that you simply do not get from reading the instructions on a tin. Some of those details are not obvious -- and a few of them matter quite a lot.

You can see zigzag marks in the fabric at the start of the video -- the signs of someone having a go with a domestic pressure washer before bringing it to us. You will see Connor use a pressure washer in the clean too, but there is a critical difference: our machines are low pressure, high volume. A domestic pressure washer is the opposite -- low volume, very high pressure -- and that jet can cut straight through a convertible roof fabric and destroy it permanently. If you are going to attempt a roof clean at home, a hose pipe and a soft brush are safer than a pressure washer from a hire shop.

Connor does a thorough job here and the result is exactly what you would hope for. You will also see him applying the protection coating with a brush rather than a trigger spray. Most off-the-shelf products tell you to spray it on -- we have tried that, and it is not as effective. A brush breaks the surface tension and works the product into the fibres properly, so the fabric is waterproofed all the way through rather than just across the surface. It takes longer but the coating performs better for it.

After the clean and coating the car also got an exterior detail as standard -- cleaning a roof generates mess across the whole car, so we always include it. The owner also took advantage of a special offer and added a boutique wax finish to the paintwork. We rotate the wax we use depending on what is current and what we rate -- it has been Autoglym, P21S and Fireball products at various points -- but the principle is the same: a proper hand-applied wax on freshly detailed paint, so the car leaves looking as good as it possibly can. The two-year nano coating deepens the colour and gives the fabric a sheen in sunlight. It came up a lovely blue.